Materials Science and Engineering A 478 (2008) 140–146 Determination of mechanical properties of parallelepiped materials embedded in solid medium and deformed under confining pressure A. Mussi ∗ , L. Thilly, J. Rabier, J.L. Demenet Laboratoire de M´ etallurgie Physique, UMR 6630 CNRS, Universit´ e de Poitiers, SP2MI, Av. M. et P. Curie, 86962 Chasseneuil Futuroscope Cedex, France Received 9 January 2007; received in revised form 22 May 2007; accepted 25 May 2007 Abstract Most hydrostatic pressure deformation techniques necessitate the use of a confining medium to apply the pressure. In the case of solid confinement, the embedding medium may modify the specimen stress tensor hydrostaticity. In this study, parallelepiped specimens deformed under gaseous confining pressure with the Paterson press, are embedded in cylindrical jackets. Finite element modelling shows that the pressurization of the ‘sample + jacket’ assembly generates a pre-compression stress of the sample before any deformation test. The evolution of the pre-compression stresses with the sample and jacket Young’s moduli ratio, the sample and jacket yield stresses ratio and the spacing between sample and jacket, are characterized. This modelling is applied to 4H-SiC deformed in the brittle regime with the Paterson press as an example. © 2007 Elsevier B.V. All rights reserved. Keywords: Confining pressure; Paterson press; Compression test; Finite element modelization; 4H-SiC 1. Introduction The mechanical properties of brittle materials are difficult to measure because of crack nucleation and propagation. In order to reduce this phenomenon, mechanical tests have to be performed under confining pressure. Griggs [1] have designed an apparatus in which the sample is confined inside a solid medium under compression to apply the confining pressure. This device generates confining pressures reaching several GPa. More recently, Cordier [2] used multi-anvil apparatus to induce plastic deformation in minerals at very high pressures attaining tens of GPa. However, because of the solid confining medium, these two devices produce stress inhomogeneities on the sam- ple prior to deformation during the pressure build-up. To bypass this problem, Paterson [3,4] conceived a device which generates hydrostatic pressure using a gas, namely argon. In addition, the load cell and the deformation piston are located inside the pres- sure vessel; as a consequence, the friction between the confining medium and the deformation piston is zero and the compression load applied to the sample is precisely measured. However, for security reasons applying to gaseous pressurised devices, the ∗ Corresponding author. Tel.: +33 5 49 49 74 55; fax: +33 5 49 49 66 92. E-mail address: alexandre.mussi@ext.univ-poitiers.fr (A. Mussi). confining pressure is rather small as compared to the previously described systems: up to 0.5 GPa. In its design, the Paterson press, initially devoted to the study of minerals and rocks (cored samples), is composed of several compression cylinders and pistons made with alumina or stabilized zirconia: the whole geometry imposes the use of cylindrical samples. However, for the study of brittle materials such as semi-conductors at low temperature, it is easier to machine the sample with a parallelepiped shape. Furthermore, parallelepiped specimens enable internal plasticity study via the post mortem analysis of glide lines on their faces. Consequently, the parallelepiped sam- ples must be embedded in cylindrical jackets which introduce unavoidable spaces between these two elements. The system ‘sample + jacket’ is first pressurized then deformed while the compression stress–strain curve is recorded thanks to the inter- nal load and displacement cells. Since the recorded data are related to the composite system ‘sample + jacket’, it is neces- sary to separate the contribution of the studied sample from the one of the jacket, with known mechanical properties. Therefore, the present paper deals with the determination of accurate mechanical properties of materials deformed with the Paterson device and embedded into jackets. In a first section, the application of the pressure onto the system ‘sample + jacket’ has been modelled by the finite elements method to compute the stress tensor developed into the sample and study the effect 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.05.119